In welding two pipes together, it is often advantageous to counterbore one pipe end. Precision and accuracy are desired when machining pipe ends, particularly when automatic or semi-automatic welding is utilized to join the pipe ends. The machining device must be held firmly in relation to the pipe in order to achieve these results. Further, in many instances a pipe in the field is out of round due to rough handling or manufacturing defects. Also, weld seams along the length of the pipe may provide an irregular surface. It is desirable that the machining tool follow the inner surface of the pipe with high precision to ensure uniform machining.
Various devices are known in the art for performing end surfacing, particularly counterboring on pipes and other elements. Such an end surfacing machine is described in U.S. Pat. No. 3,733,939 to Paysinger, et. al. which discloses an apparatus for preparation of large pipe ends for welding girth joints. The device is comprised of a case shaped, double ended aligning clamp which axially aligns and firmly supports a rotatable face plate. This plate carries multiple cutting tools and guide rollers, mounted on spring-biased pivoted arms which permit radially inward and outward motion of the tools and rollers with respect to the pipe end. The face plate is power driven around the axis of the clamp. Each pivoted arm carries a cutter closely coupled with a precision guide roller.
A firm backing surface to guide the machining tool during operation is desired. Means such as this are known in the art. However, such means are complicated requiring many parts and much set up time. Therefore, there is a need for a counterbore attachment that is simple in construction and easy to operate.